The present invention relates to a reinforcing device as well as a method for reinforcing beams.
When rehabilitating supporting structures in existing buildings, the supporting structures often are to be adapted for new load cases that exceed the former dimensions. In order to avoid replacing a supporting structure completely in such cases, methods and devices for reinforcing such an existing supporting structure have been found. Such supporting structures can be walls of conventional design made of brick, reinforced concrete walls or beams, or beams made of wood, plastic, or steel, for example.
Reinforcement of such supporting structures with steel plates added later has been known for a long time. The steel plates, namely strips of sheet steel or steel panels, are glued to one or both sides of the supporting structure, preferably on the side of the supporting structure subjected to tension. The advantage of this method is that it can be implemented relatively quickly, but the method imposes strict requirements on the adhesive. In other words, the preparation of the parts and the performance of the adhesion process must take place under precisely defined conditions to achieve the desired effect. Problems, and especially corrosion problems, arise when supporting structures such as bridge beams are to be reinforced in this manner in the open. Because of the relatively high weight and the production of such steel panels, the maximum length that can be used is limited. Likewise, for reasons of space, installation in closed spaces can be problematic when the rigid steel panels cannot be transported into the space in question. In addition, the steel plates must be pressed against the supporting structure to be reinforced until the adhesive sets in “overhead” applications. This also results in high cost.
It is known from French Publication 2 590 608 to use tensioning means in the form of strips of metal or fiber-reinforced plastic with anchors at the ends. In this embodiment, however, there is no flush connection between the tensioning means and the supporting structure. Instead, a connection with the supporting structure is provided only in the two end anchoring points of the tensioning means. Clamping means of this kind are conventionally included when planning the supporting structure, because retrofitting is practically impossible or can be done only at very high cost, since corresponding channels in the supports must be prepared for the clamping means.
Recently, carbon panels (CFK panels) have been glued to the tensioned sides of the supporting structure and, thus, the carrying capacity of such structures is subsequently improved by increasing the supporting resistance and ductility. Advantageously, the simple and economical application of such panels, which have a higher strength than steel panels with a far smaller weight, is provided, and the panels are simpler to install. The corrosion resistance is also better so that such reinforcements are also suitable for reinforcing supporting structures in the open. However, the end anchoring of the panels has proven to be particularly problematical. The danger of the panels coming loose is particularly great in this areas and there is a problem in that the force is introduced from the end of the panel into the beam.
A solution is this regard is known from international publication WO96/21785; here, a bore that runs at an obtuse angle or a wedge-shaped recess is made in the beam in which the ends of the CFK panels are inserted and pressed against the beam, possibly by clamps, loops, plates, etc. This results in an improvement in loosening behavior and an improved initiation of the force from the beam into the panel. However, such CFK panels are glued without pretensioning, in other words flexibly, to the beam. As a result, much of the reinforcing potential of these panels is not utilized, since panels begin to provide support only after they exceed the basic load, in other words under stress from the useful load itself.
In order to utilize the panels better, the idea has arisen of gluing them pretensioned to the beam. One known solution 1 in this regard provides that short steel plates are glued to the ends of the CFK panels on both sides. The steel plates are then pulled apart and the CFK panels are pretensioned, and this pretensioned arrangement is glued to the beam to be reinforced. After the glue dries, the panels are pressed at the ends against the beams by plates, loops, etc. and the ends are then cut off with the steel plates. This method, however, is very expensive and cannot be used in all applications. The method of anchoring the panel ends described above is also not suitable for pretensioning at building sites.
Hence, the goal of the present invention is to provide a CFK reinforcing panel in which the introduction of force from the beam into the ends takes place in such fashion that separation becomes practically impossible and which is also suitable for pretensioning.
This goal is achieved by splitting the ends of a CFK panel into at least two and preferably three or more end; strips. In this way, the surface for connection to an end element is increased considerably. As a result, there is a good initiation of the force into the ends of the CFK panel which can also be pretensioned in simple fashion by such an end element. The end element in block form can be either inserted into a depression in the beam or, in the preferred embodiment, with a wedge-shaped split with a flat or rough bottom, can also be glued and/or doweled or simply bolted flush to the beam. It is this embodiment that is preferably suited for pretensioning which preferably takes place directly through the beam part. For example, this can be done by tensioning against a fitting inserted into the beam.
The splitting of the ends of the CFK panels preferably takes the form either of strips on top of one another or strips that are side-by-side, or in a combination of these two versions.
The ends of the CFK panels can advantageously be split at the building site itself to the required length and dimensions. This makes this system highly universal for the reinforcement of practically any beam, and the system can be employed with or without pretensioning.
The invention is described in greater detail below with reference to the figures in the enclosed drawings.